In a recent tweet, our new president wrote:
At 9:00 P.M. @CNN, of all places, is doing a Special Report on my daughter, Ivanka. Considering it is CNN, can't imagine it will be great!— Donald J. Trump (@realDonaldTrump) January 17, 2017
Sadly, Trump knows nothing about grammar. If he did, he’d have written:
“My daughter Tiffany” (without the comma).
“My daughter Tiffany” means he has multiple daughters, whereas “My daughter, Tiffany” means he has only one.
Commas can kill.
Here’s another example:
“If you’re like to meet my friend, Susan, please join us for dinner.”
means I have only one friend.
“If you’d like to meet my friend Susan, please join for us dinner.”
means Susan is one of my friends.